Check the paths of node and ng to ensure availability

* The script assumes ng has been installed and added to the user path.
  However, this is not always the case, resulting in 'ng command not found'
  errors when trying to run the beetle-studio image.

* Checks the existence of both node and ng and ensures that the latter is
  using the one installed by npm in beetle-studio's own node_modules
  directory.

ngapp/start.sh

@@ -1,5 +1,15 @@
 #!/bin/bash
 
+# Check node is available
+command -v node >/dev/null 2>&1 || { echo >&2 "Requires 'node' but it's not installed.  Aborting."; exit 1; }
+
+# Check ng is available - should be post 'npm install'
+NG="node_modules/.bin/ng"
+if [ ! -f ${NG} ]; then
+  echo "Error: cannot find 'ng' so nothing can be executed... exiting"
+  exit 1
+fi
+
 #################
 #
 # Show help and exit
@@ -26,7 +36,7 @@ done
 shift "$(expr $OPTIND - 1)"
 
 if [ "${DEV}" == "1" ]; then
-  ng serve --host 0.0.0.0 --port 8080 --disable-host-check
+  ${NG} serve --host 0.0.0.0 --port 8080 --disable-host-check
 else
-  ng build && node ./server.js
+  ${NG} build && node ./server.js
 fi